This invention relates in general to a circuit for controlling the number of fluorescent lights turned on in a bank of such lights.
There are circumstances, primarily in order to save power, in which it is desirable for the fluorescent lights in commercial and industrial establishments to be dimmed, or selectively turned off, to provide less than maximum light output.
Full 100% light levels are required when the establishment is in full operation with a full complement of personnel. But there are times when substantially lower light lower levels are desired, particularly when the establishment is not operating. For security and safety reasons, there is usually a desire to maintain some light level.
There are known ways of dimming the lights through the use of electronic dimming ballasts. These are expensive techniques and are thus frequently not used.
There are known techniques to selectively turn off fluorescent tubes through coded signals delivered on a carrier signal. This technique is expensive and is subject to signal degradation and errors due to noise and extraneous signals picked up by the line which delivers the carrier signal.
Accordingly, what is required, and which is an object of this invention, is an inexpensive, simple to use system, secure from failure due to external signals, to provide an ability to selectively turn off fluorescent lights in a set of fluorescent lights.
Definitions
The term xe2x80x9clight unitxe2x80x9d is used herein to refer to the unit consisting of a ballast and the fluorescent tubes controlled by that ballast. Normally a light unit will be a single ballast and two tubes. There are times when a light unit can be a single ballast and one tube. Applicant is not aware of any situation where a single ballast controls more than two tubes. However, it should be understood herein that the term light unit refers to a single ballast and whichever number of tubes are controlled by that ballast.
A light fixture is normally composed of a plurality of such light units. Four light units for a fixture is very common. Such a fixture would have four ballasts and eight fluorescent tubes. But any number of light units can be contained in a single fixture.
In brief, the fluorescent lights in a fixture are selectively turned on or off by virtue of energization of relays coupled thereto. The relays control the state of normally open switches. The switches close when the relay is turned on to connect the associated light unit (i.e. fluorescent tubes and ballast) to a source of power. When open, the switch disconnects the light unit. The relays, in turn, are energized selectively either individually or in groups by the position of an arm on a manually operated rotary switch.
For example, in a four ballast fixture, one light unit can be continuously connected to the power line in order to provide at least 25% illumination.
A second light unit is connected to the power line through a first relay to provide an additional 25% illumination when that relay is energized and its associated contact is closed. This provides a total of 50% illumination.
Third and fourth light units are coupled to the source of energy by virtue of a second relay. When energized, the second relay closes associated switches and turns on the third and fourth light units to provide a 50% illumination, which with the first light unit provides a total of 75% illumination.
When both relays are energized, 100% illumination is provided.
The relays are connected to energizing power through the terminals of a rotary switch. Diodes block and steer current flow to the relays depending on the rotary switch terminal selected by the user.